引起舟曲特大泥石流灾害的"8·8"暴雨过程中尺度特征分析

利用常规气象资料以及FY-2E气象卫星云图、多普勒天气雷达资料和NCEP每6h一次的1°×1°格点资料,采用天气学诊断分析的方法,对2010年8月7—8日出现在甘肃省舟曲县的一次局地突发性致泥石流暴雨进行了诊断分析。结果表明:此次暴雨是在高空短波槽、东风倒槽、低涡切变线、副热带高压和地面冷空气的共同作用下发生的。对流云团发展生成MCS是暴雨发生的直接原因。对流云降水回波的发展和增强与降水强度的变化有很好的对应关系。来自孟加拉湾和东海的暖湿空气是此次暴雨的主要水汽来源。中低层辐合,高层辐散的配置和垂直涡度的显著增大,为本次暴雨的发生提供了必要的动力条件。暴雨中心位于700 hPa等假相当位温线密集带的西南侧边缘,暴雨是伴随着对流有效位能和大量不稳定能量的有效释放而发生的。倾斜涡度的活跃发展,条件性对称不稳定机制的形成可能是导致此次暴雨发生的主要触发机制。

Mesoscale analysis on severe torrential rainstorm causing debris flow disaster in Zhouqu county on 8 August 2010

Diagnostic analysis was performed on a local and abrupt rainstorm causing debris flow disaster in Zhouqu county of Gansu province during 7-8 August 2010 by using the conventional meteorological data,infrared nephogram from FY-2E stationary meteorological satellite,Doppler weather radar data and NCEP data of 1°×1° with 6 h intervals.The results indicated that the heavy rainfall happened because of many conditions working together,including short-wave trough at high altitudes,easterly reverse trough,low vortex with shear line,the subtropical anticyclone and the ground cool air.The immediate cause of heavy rainfall occurrence was mesoscale convective system(MCS) that developed from convective cloud cluster.Development and strengthening of radar echo of convective cloud precipitation correlated well with tendency of precipitation intensity.The moisture mainly moved from the Bay of Bengal and East China Sea.The dynamic conditions were provided by the significant increase of vertical relative vorticiy and the configuration of the convergence at the middle-low level and divergence at the upper level.The center of heavy rainfall was located in southweat part of the dense isoline of potential pseudo-equivalent temperature(θse) at 700 hPa.The heavy rainfall was followed by the release of convective available potential energy(ECAP) and some other instability energy.The forming of the conditional symmetric instability(CSI) mechanism and active development of slantwise vorticity may be the important triggering mechanism of heavy rainfall.